Warning: contains spoilers for Avengers #50!
In its landmark fiftieth issue, Avengers has revealed the existence of a new class of heroes in the Marvel multiverse - Omni-Avengers. The term comes from one of the Invincible Ant-Man's Deathlok army - reanimated zombie-cyborgs sent out across Marvel's many alternate realities to gather an army against the Multiversal Masters of Evil. One Omni-Avenger has been revealed so far - a choice that may give away crucial details about this new category, and even hint at the other heroes who will make the cut in future issues.
Introduced in Free Comic Book Day: Avengers/Hulk #1, the Multiversal Masters of Evil are villains from different realities who have made it their mission to wipe out the Avengers across all realities. The villains are huge in scale, and each is a major threat on their own, from the Ghost Goblin (a Ghost Rider/Green Goblin hybrid who weaponizes the skulls of defeated Spirits of Vengeance) to the Black Skull (a version of Red Skull who has gained control of the Venom symbiote.) Fighting back is the Invincible Ant-Man - a variant of Tony Stark who mans the Avengers Tower at the center of creation, sending his Deathloks out to recruit heroes and, apparently, identify Omni-Avengers.
In Avengers #50 from Jason Aaron, Aaron Kuder, Carlos Pacheco, Ed McGuinness, and Javier Garron, Ghost Rider Robbie Reyes is identified as an Omni-Avenger by a Deathlok who then manipulates his powers to traverse the multiverse, confirming that the young hero has some serious untapped power. It's unclear from this issue exactly what makes Robbie an Omni-Avenger - is it his newly revealed power level, his place as a legacy hero, or his ability to travel between realities? The most obvious answer is that the Ghost Rider is one of seven archetypal heroes whose symbols have peppered Aaron's time on Avengers, but this alone isn't enough - when Valkyrie arrives with another Deathlok, it indicates there are no Omni-Avengers present, despite Black Panther being another of these symbolic heroes.
The symbols in question appear to denote Thor (or Odin - another wielder of Mjolnir), the Phoenix, Iron Fist, Black Panther, the Sorcerer Supreme, the Starbrand, and the Ghost Rider. Of course, these symbols also correspond to the Avengers of 1,000,000 BC, and thus the oldest supernatural forces who have stood in protection of Earth since the dawn of humanity, but previews of Avengers Forever - a miniseries running alongside Avengers to depict the multiversal battle for survival - show that they're relevant to the Invincible Ant-Man's search.
There is still a way in which the symbols could denote Omni-Avengers - it could be the case that the Invincible Ant-Man will be searching for the perfect version of each archetype from different worlds in the multiverse. Robbie Reyes may not have been chosen because he's a Ghost Rider, but because he's the Ghost Rider, with prior comics implying that his powers far exceed previous Spirits of Vengeance. This would also serve to make the Multiversal Masters of Evil's mission more specific, as they could be killing off Avengers in order to get the seven key Omni-Avengers. Kid Thanos has already revealed that it's his mission to "kill all of the Odins," and it would make sense that he doesn't just hate every version of the All-Father, but is tasked with wiping out the Omni-Avenger symbolized by Mjolnir.
The idea of seven Omni-Avengers magically symbolizing the team - and able to make or break its destiny across the multiverse - would give the otherwise chaotic story unfolding in Avengers and Avengers Forever a clear purpose, with Tony's variant fighting to unite them as the Multiversal Masters of Evil and Mephisto strive to kill them off, but for now, it's just a theory. All fans know for sure is that Robbie Reyes' Ghost Rider is one of a rare class of hero known as Omni-Avengers, and that they're certain to meet more such heroes as the newest Avengers saga unfolds.